1. Field of the Invention
The present invention relates to a micro pressure sensor and, more particularly, to an isolated micro pressure sensor suitable to be used in biological field or in erosive environment.
2. Description of Related Art
Many micro pressure sensors such as piezo-resistive micro pressure sensors, electric-capacitive micro pressure sensors, piezoelectric micro pressure sensors, or resonant micro pressure sensors are widely used in industry and our daily life. Among them, the piezo-resistive micro pressure sensors are mostly used in automobile and medical field for their advantages of small volume, low cost, and good performance. In the conventional manufacturing process for the piezo-resistive micro pressure sensors, however, complicated photolithography processes and various photo masks are needed to produce various forms of piezo-resistive micro pressure sensors for meeting the specifications under different operational pressure ranges. This conventional method requires higher cost, and takes longer lead-time to fabricate various forms of sensors.
With reference to FIG. 1, the structure of conventional piezo-resistive micro pressure sensors is shown. The conventional piezo-resistive micro pressure sensor comprises a glass substrate 100 having a ventilation channel 110 and a silicone substrate 120 having a cavity 130, a plurality of piezo-resistors 140 and a diaphragm 150. The piezo-resistors 140 are connected to metal pads 160 through conductive circuits formed on the substrate. When fluid or gas flows into the ventilation channel 110, the pressure will be passed through the cavity 130, and the diaphragm 150 will be forced to deform and to pass the strain to the piezo-resistors 140. The piezo-resistors 140 further transform the strain into electric signals and output the electric signals to gold wire 170 through the metal pads 160.
However, the sensing elements (the piezo-resistors and the conductive circuits) of the conventional piezo-resistive micro pressure sensors as shown in FIG. 1 are exposed to the environment media. Hence, the conventional piezo-resistive micro pressure sensors are not suitable to implement in some corrosive conditions, such as in erosive fluid or in biological environment (e.g. in blood).
U.S. Pat. No. 6,308,575 describes a manufacturing method for the miniaturization of silicon bulk-machined pressure sensors. This patent only provides a micro pressure sensor small enough to implant into human or animal body, but the pressure sensing elements included in such pressure sensors are still exposed to the environment. Therefore, the stability of the micro pressure sensor decreases and not suitable for biomedical use, either.
Therefore, it is desirable to provide a novel isolated micro pressure sensor to mitigate and/or obviate the aforementioned two problems.